The first thing the app has to do to be able to measure is it has to detect a horizontal plane.  In this case it is a floor.  Here are some things you can do:

  1. Make sure you are pointing the device at the floor
  2. Move the device slowly forward and backward still pointing at the floor.  You can even walk a few steps if you like.
  3. Try turning on more lights
  4. The floor might be too plain.  For example, an all white carpeted floor with no texture.  The detection needs to see "variances" in the floor to calibrate.  Try moving to a different room or introducing some "variances" onto the floor (e.g. throw rug) that still maintains a flat surface.
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